U.S. Pat. No. 5,005,369, assigned to the assignee hereof, discloses a refrigerant recovery and purification system that includes a compressor having an inlet coupled through an evaporator and a solenoid valve to the refrigeration equipment from which refrigerant is to be recovered, and an outlet coupled through a condenser to a refrigerant storage container or tank. Refrigerant may be withdrawn from the storage container and pumped, either by the compressor or by a separate liquid refrigerant pump, through a filter/drier for removing water and other contaminants, and then returned to the storage container. A pressure differential valve receives a first pressure input from a refrigerant bulb positioned for heat exchange with refrigerant fed to the storage container, and thus indicative of temperature of refrigerant within the container itself. A second input to the valve is indicative of refrigerant/air vapor pressure within the container. The valve is coupled to a purge port on the container for automatically venting air from within the container when the pressure differential between the valve input ports exceeds the threshold setting of the valve. In a modified embodiment, a differential pressure gauge receives the first pressure input indicative of refrigerant temperature and the second input indicative of refrigerant/air vapor pressure within the container, and a manual valve is coupled to the container purge port for manipulation by an operator when the gauge indicates excessive pressure differential.
U.S. Pat. No. 5,063,749, also assigned to the assignee hereof, discloses a refrigerant handling system having both air purge and multiple refrigerant capabilities. A refrigerant bulb is positioned for heat exchange with refrigerant fed to the storage container as in the earlier patent. A double-needle pressure gauge has a first port coupled to the refrigerant bulb and a second port coupled to the container. The gauge needles thereby indicate vapor pressure of refrigerant fed to the container and refrigerant/air vapor pressure within the container. The gauge is provided with multiple scales calibrated for differing types of refrigerant, so that an operator knowing the type of refrigerant under service may observe the gauge, determine the pressure differential between the container refrigerant/air vapor pressure and the refrigerant saturation pressure, and manually purge air from within the container when such pressure differential exceeds the desired level.
Although the inventions disclosed in the above-noted patents address and overcome problems theretofore extant in the art, further improvements remain desirable. For example, although the automatic and manual air purge techniques disclosed in U.S. Pat. No. 5,005,369 operate well for a specific type of refrigerant, this technique is not well suited for use in conjunction with multiple refrigerants because the refrigerant/air vapor pressure in the storage container does not compare with the saturation pressure within the bulb properly to indicate partial pressure of air within the container unless the refrigerant in the bulb is of the same type as that in the container. The invention of U.S. Pat. No. 5,063,749 provides such multiple refrigerant capability, but has the disadvantage that comparison of two needle readings is required, and that the coaxially mounted bourdon tube gauge produces additive error in the two gauge readings.
It is therefore a general object of the present invention to provide a refrigerant handling system with air purge capability that exhibits improved accuracy as compared with the systems disclosed in the '749 patent, and/or that is capable of handling multiple differing types of refrigerants as compared with the systems disclosed in the '369 patent. Another object of the present invention is to provide a refrigerant handling system with both air purge and multiple refrigerant capabilities in which the air purge gauge can assist an operator in identifying the type of refrigerant under service and/or an empty storage container.